First Post - Circuit Design Need Help

[douglee25]

Hello everyone! This is my first post here as I'm looking for some eletronics help. EE def. wasn't my strong point in college, hence why I became an ME Please bare with me if this sounds like a simple question.

The task:

On my 21ft boat I'm trying to build a circuit that pulses a signal wire coming off the ignition coil. In other words, if take the negative terminal on the coil and put it to ground, the engine shuts off.

What I'm looking to do is to be able to hold in a N.O. momentary switch while I'm shifting the boat into gear and have the engine stumble (not stall) by pulsing this wire to ground. When I release the switch, the engine should run normally.

I have already mounted the switch near the shifter control and just wired one end to ground and the other end to the neg. side of the coil. Obviously if I hold the switch in for too long, the engine stalls. I can pulse the switch with my finger, but that gets old.... hence the design of the circuit. Would this fall under the oscillating circuit category or something?

Please help. Thanks for your time.

Doug

 

[philba]

let me play back what I think you are asking for: you want a circuit that grounds the ignition wire for a series of short periods while you press a switch.

do you have a power source? what is it? I am assuming that the wire you want to ground has fairly high voltage. do you know what it is? What is the approximate rpm of the motor when you are shifting? when you manually pulse the button, how many times a second and for how long do you hold it down for each pulse?

it would be fairly simple to make something but the above details are important to getting it to work correctly.

 

[douglee25]

let me play back what I think you are asking for: you want a circuit that grounds the ignition wire for a series of short periods while you press a switch.

do you have a power source? what is it? I am assuming that the wire you want to ground has fairly high voltage. do you know what it is? What is the approximate rpm of the motor when you are shifting? when you manually pulse the button, how many times a second and for how long do you hold it down for each pulse?

it would be fairly simple to make something but the above details are important to getting it to work correctly.

To answer your questions (in no particular order)....

The negative side of the coil should read anywhere from 1 - 6 Volts (this is the wire I want to ground). This negative terminal is also where the tachometer lead is attached to. After I construct the circuit, I want to hold in the switch so the negative side of the coil is pulsed to ground. The pulse needs to be quick enough so not to stall the engine (I'm sure much quicker than 1 second pulses). The engine rpm is about 650 rpms to 700 rpms. I have a power source if need be (12 Volts).

Thanks for your time.

Edit: Coil voltage on the negative side is between 1 - 14 Volts. Disregard 6 volts.

Doug

 

[philba]

ok, so I would use a relay and a 555 timer in async mode. The "pulse" switch would connect the circuit to +12V. The 555 output would drive a 12V relay. The relay would short your ignition to ground (or disconect it?). It would make a clicking sound but in that environment, you probably wouldn't hear it. The reason for the relay is that it will give you much more isolation from electrical noise than anything else.

Lets call the pulse duration 500 mS - you can make it adjustable. The pulse frequency is probably around 1 per second (?). can be made adjustable, too. though the 555 timer is a little tricky this way (changing one changes the other) but I suspect it's not that critical.

is that enough for you to put something together?

 

[douglee25]

ok, so I would use a relay and a 555 timer in async mode. The "pulse" switch would connect the circuit to +12V. The 555 output would drive a 12V relay. The relay would short your ignition to ground (or disconect it?). It would make a clicking sound but in that environment, you probably wouldn't hear it. The reason for the relay is that it will give you much more isolation from electrical noise than anything else.

Lets call the pulse duration 500 mS - you can make it adjustable. The pulse frequency is probably around 1 per second (?). can be made adjustable, too. though the 555 timer is a little tricky this way (changing one changes the other) but I suspect it's not that critical.

is that enough for you to put something together?

I did some research on these items that you mentioned but due to my lack of electrical knowledge, I'm not having much luck. I'm OK with auto relays but one we get into the 555 timer, I'm lost. I'll paypal you a few bucks if you could get me a wiring diagram with adjustability on the pulse duration and the frequency. This sounds like what I'm looking for. Thanks again.

Doug

 

[DirtyLude]

If you will accept a commercial solution, these things are real popular for motorcycles. Most assume that you are using a sequential shifter, so the implementation may need to be modified for your boat.

if you google 'motorcycle quick shift' and/or other related words, you will get multiple hits for these products.

 

[Jerry Brady]

If you look at the circuit in this thread:

https://www.electro-tech-online.com/threads/lighting-up-a-model-circuit-help-review-needed.21475/

You'll see a 555 timer circuit. The switching diode on the far left makes it so you can control the on and off timing independently. Without it, as philba said, changing one value affects the other.

Googling "555 timer calculator" will help you determine the resistor values and you can pick up the parts from your local supply shop pretty cheaply.

Edit: The "pulse output" is what you would use to drive the relay.

I hope this helps.

 

[Roff]

If you look at the circuit in this thread:

https://www.electro-tech-online.com/threads/lighting-up-a-model-circuit-help-review-needed.21475/

You'll see a 555 timer circuit. The switching diode on the far left makes it so you can control the on and off timing independently. Without it, as philba said, changing one value affects the other.

Googling "555 timer calculator" will help you determine the resistor values and you can pick up the parts from your local supply shop pretty cheaply.

Edit: The "pulse output" is what you would use to drive the relay.

I hope this helps.

That's an astable circuit. He needs a monostable. There are lots of sites to be found by Googling "555 monostable". Check out some of them, like https://www.eleinmec.com/article.asp?4.

 

[douglee25]

That's an astable circuit. He needs a monostable. There are lots of sites to be found by Googling "555 monostable". Check out some of them, like https://www.eleinmec.com/article.asp?4.

I'm reading up on the 555 timer again but I do believe I need a 555 astable circuit because I want the circuit to pulse multiple times while I hold the button in vs. pulse once with each button push, no?

Edit: So supply voltage to the 555 is 12v from the battery. + to pin 8 and - to pin 1. Pin 2 hooks up to the N.O. switch and the other end of the switch gets grounded. Pin 3 is the output to the coil on the relay (#87 4 pin auto relay). Be sure to use a diode on the output to avoid back emf. The other side of the coil gets grounded, the normally open side of the relay gets the - wire off the ignition coil, and the other end of the relay also gets grounded. I'm lost at the part where the variable pots and capacitors come into play to adjust the frequency and duration.

In case this wasn't clear, when I hold down the N.O. switch, I want the circuit to continually pulse until I release the switch.

Doug

 

[Roff]

I'm reading up on the 555 timer again but I do believe I need a 555 astable circuit because I want the circuit to pulse multiple times while I hold the button in vs. pulse once with each button push, no?

Doug

A thousand pardons to you and to Jerry Brady. I thought your eventual plan was to actuate the switch with a mechanical linkage to the shifter (like the motorcycle quick shifters), so you would only need the ignition shorted for a few hundred milliseconds at most.
I had a friend who made one back in the late '70s for his pumped up Kamakazi (it was a Kawasaki, but he was drag racing it). He used a microswitch that was actuated by the shifting arm. Killing the ignition, as you probably know, removed the torque loading on the transmission momentarily, allowing him to shift without using the clutch or backing off the throttle. It worked in a trial, but he was afraid it would fail at the worst possible time, breaking his bike, or worse, his neck, so he removed it without ever using it in a race.

 

[DirtyLude]

Why do you want multiple times? From what I understand, this is a simple quick shift, which means you want to cut the ignition to cut the load on the transmission for the time of the shift. A one time only event.

 

[douglee25]

Why do you want multiple times? From what I understand, this is a simple quick shift, which means you want to cut the ignition to cut the load on the transmission for the time of the shift. A one time only event.

I figured it would be easier to just hold in the switch while I shifted the boat into gear. I suppose I could get the 555 timer to pulse for a certain period of time, but if I didn't shift into gear soon enough (ie got distracted doing something else just prior to shifting) then I would have to hit the switch again. If I am able to just hold in the switch and have the engine stumble for as long as I hold it in, then I would think this may be more suiting to my application.

Doug

 

[douglee25]

I will post this again as it may have been lost in the previous edit...

Edit: So supply voltage to the 555 is 12v from the battery. + to pin 8 and - to pin 1. Pin 2 hooks up to the N.O. switch and the other end of the switch gets grounded. Pin 3 is the output to the coil on the relay (#87 4 pin auto relay). Be sure to use a diode on the output to avoid back emf. The other side of the coil gets grounded, the normally open side of the relay gets the - wire off the ignition coil, and the other end of the relay also gets grounded. I'm lost at the part where the variable pots and capacitors come into play to adjust the frequency and duration.

Unless this part wasn't clear or if I'm going about this the wrong way (please advise) when I hold down the N.O. switch, I want the circuit to continually pulse until I release the switch.

Doug

 

[Jerry Brady]

Take a look here:

**broken link removed**

It gives the formulas for computing the high (mark) time and the low (space) time. You can go form there.

I hope this helps.

 

[kamdy]

Hi
Is your boat engine controlled by ECU ? If it is so the idea of shorting the negative wire of the Ignition coil is very dangerous because it can cause damage to the ignition coil driver in the ECU. It would be better to control the signal RPM sensor of the engine by disconnecting it from ECU by using a switch or a 555 that control a relay this methode will give the same resuly without causing any damage to the ECU

Kamal Daniel

 

[philba]

this is close to what you want. sorry for the semi-ugly schematic. I've never figured out to draw clean ones using the 555. I set up the relay to break the connection but you can do what you want there. Pulse width and frequency are adjustable. I didn't know how clean your 12V source is so I added a 220uF and 100nF caps. I put a diode in series with the 12V source to protect against battery reversal. R1 controls pulse width, R2 controls frequency. I'd use small trimmer pots. R3 and R4 are optional but are there to avoid running the trimmers to 0. I would find a sealed 12V relay with coil current below 50 mA or so. The switch simply switches power to the unit so it is only drawing current when you use it.

On the relay, you should not switch the ignition coil current.

 

[douglee25]

this is close to what you want. sorry for the semi-ugly schematic. I've never figured out to draw clean ones using the 555. I set up the relay to break the connection but you can do what you want there. Pulse width and frequency are adjustable. I didn't know how clean your 12V source is so I added a 220uF and 100nF caps. I put a diode in series with the 12V source to protect against battery reversal. R1 controls pulse width, R2 controls frequency. I'd use small trimmer pots. R3 and R4 are optional but are there to avoid running the trimmers to 0. I would find a sealed 12V relay with coil current below 50 mA or so. The switch simply switches power to the unit so it is only drawing current when you use it.

On the relay, you should not switch the ignition coil current.

Ok, I really do appreciate your drawing. I'm trying to learn the notation but I still have a couple questions.

1. Notation JP1 and JP2 means?
2. OEG-PCH means?
3. I'm confused by what you mean when you say you should not switch the ignition coil current? The output on pin 3 goes to the relay coil (4 pin relay) and the other side of the coil gets grounded. Now the ignition coil leg goes to the one side while the other leg on the relay is also grounded, no? So when the 555 timer sees the output, the output pulls the coil in on the relay which then grounds the ignition coil? Correct?
4. The switch sees 12v which then goes to pin 8, correct? I see your notation by JP2 says the switch gets grounded, but it should just go to pin 8 and not ground, correct?
5. Would these 100k trim pots be acceptable? https://www.radioshack.com/product/...62287&cp=&origkw=pot&kw=pot&parentPage=search

Thanks again for your time.

Doug

 

[philba]

1) JP is a connector. I usually use screw terminals but you can use anything. the barrier terminal on this page might be good: https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=440858
2) OEG-PCH is the type of relay I used to draw the circuit. Its a fairly cheap relay, I'd recommend a sealed unit. sorry for the confusion.
3) The coil voltage to the spark plugs will be fairly high. Most relays aren't rated for higher voltage. it may well be fine but I don't know. I'd try to switch lower voltage going to the coil.
4) jp2 has 2 connectors the top one goes to +12V, the bottom one goes to the minus terminal (basically 0 but you might think -12V).
5) just about any trim pots will work. those aren't trimmers though. yes, they will work but I was thinking more along the lines of https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=241496
the idea is that you adjust the pulse width and frequency with a screw driver and then never touch them again. Maybe even drop a little nail polish on them the keep them from moving.

You can get everything from radioshack. I prefer mouser but I think Jameco.com is probably a reasonable choice for you - better pictures than mouser, better products than RS and, of course, better prices than RS.

 

[Oznog]

It's not always advisable to cut off the ignition like this and then start it again. The cylinders are still taking in a fuel/air charge and pumping it out the exhaust. It can potentially backfire.

 

[douglee25]

1) JP is a connector. I usually use screw terminals but you can use anything. the barrier terminal on this page might be good: https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=440858
2) OEG-PCH is the type of relay I used to draw the circuit. Its a fairly cheap relay, I'd recommend a sealed unit. sorry for the confusion.
3) The coil voltage to the spark plugs will be fairly high. Most relays aren't rated for higher voltage. it may well be fine but I don't know. I'd try to switch lower voltage going to the coil.
4) jp2 has 2 connectors the top one goes to +12V, the bottom one goes to the minus terminal (basically 0 but you might think -12V).
5) just about any trim pots will work. those aren't trimmers though. yes, they will work but I was thinking more along the lines of https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=241496
the idea is that you adjust the pulse width and frequency with a screw driver and then never touch them again. Maybe even drop a little nail polish on them the keep them from moving.

You can get everything from radioshack. I prefer mouser but I think Jameco.com is probably a reasonable choice for you - better pictures than mouser, better products than RS and, of course, better prices than RS.

1. Ok, got it.
2. Ok, got it.
3. The ignition coil voltage on the negative terminal is between 1 - 14 volts. Any auto #87 relay is able to handle 30 amps or so. This is a sealed unit as well. This should be work or am I still misunderstanding your information here?
4. I'm still lost on this one. The 12 volts supplied is switched via the N.O. switch. 12 volts in to one leg of the switch, the other leg of the switch to Pin 8? When the switch is pressed, 12 volts is supplied to pin 8 to power the 555 timer. Is this correct?
5. Ok, RS isn't the best choice.

Thanks again.

Doug